The present invention relates generally to the field of devices for data entry, viewing, and manipulation in computers. More particularly, this invention relates to a low cost human interface system for interactive computer simulations, most particularly a low cost human interface for a virtual reality system.
Three of the key aspects of a virtual reality interface are tracking the user's head and other body parts, sensing user input actions and display of sensory information to the user in such a way that the sensory information displayed replaces the corresponding senses arising from the physical world. Such systems are typically quite expensive.
Position and orientation of the user's head and other body parts are continually tracked in order to keep the simulation updated to correspond correctly to the user's changing point of view. Tracking technologies have been relatively high cost components of a virtual reality system, and typically involve electromagnetic transmitter/receiver systems such as manufactured by Polhemus Inc., of Colchester, Vt.
The display of sensory information from the virtual reality simulation must be proximal to the user's head at all times, so that the relative position of the display to the user's eyes and ears remains constant as the user moves. Such a system is generally termed a Head Mounted Display (HMD), though it is not limited to devices mounted directly on the head. It contains visual and auditory displays for each sense organ and has typically also been an expensive component.
Of particular interest here is the visual display portion of the HMD. Weight concerns generally dictate a liquid crystal display (lcd). The general structure of a lcd display includes a source of unpolarized light, a first polarizer, a polarization rotating array (which creates the individual pixels), and a second polarizer which serves as an analyzer. Light travels in the above named sequence. The first polarizer gives the light a uniform polarization, either in the angle transmitted by the analyzer or perpendicular to it. The polarization rotating array operates on the polarized light in a pixel-wise manner, either passing it unchanged or rotating the polarization by 90.degree.. This light then continues on to the analyzer, which in one polarization angle transmits all wavelengths, and perpendicular to that blocks all wavelengths, to leave light: and dark pixels for display. Since in an HMD the pixels are so close to the viewer's eye, many people focus on the pixels at an individual level and don't perceive the overall shapes within the image as well. For this reason a diffusion screen may be superimposed over the lcd, which slightly blurs the image and fine detail, but facilitates the perception of patterns and shapes. Understandably, not all viewers like this trade off.
Color lcds can be made by including a mask within the display, dyed with red, blue and green pixel sized dots. This-mask is lined up with the pixels of the polarization rotating array, and each grouping of three monochromatic pixels masked to form a red, blue and green pixel then forms a color pixel. This conversion to a color lcd obviously results in a 3:1 reduction in resolution.
Color versus resolution is just one of the many trade-offs that must be resolved in choosing a display. Another important consideration is whether and how much the fields of view of the right and left eyes overlap. The most natural classification is into two groups--separate images for each eye and totally shared images. Using separate images for each eye instead of a totally shared image has the advantage of allowing stereoscopic vision and improved depth perception. Unfortunately, having two separate images requires more computing power, and for an lcd of given pixel size and distance from the eye only half as many pixels are available for each image, resulting again in lower resolution.